Change cache-miss log to Warning, gate to HTTP transport only

Log a Warning (instead of Debug) when a tools/call request has no
cached tool definition, but only for StreamableHttpClientSessionTransport
where Mcp-Param-* headers are relevant. Pipe/stdio transports do not
emit this warning since headers do not apply.

Added tests:
- Pipe transport: cache miss does NOT log a warning
- HTTP transport: cache miss DOES log a warning

Author: Tarek Mahmoud Sayed

src/ModelContextProtocol.Core/Client/McpClientImpl.cs

@@ -733,7 +733,7 @@ request.Params is System.Text.Json.Nodes.JsonObject paramsObj &&
                 request.Context.Items ??= new Dictionary<string, object?>();
                 request.Context.Items[McpHttpHeaders.ToolContextKey] = tool;
             }
-            else
+            else if (_transport is StreamableHttpClientSessionTransport)
             {
                 LogToolCacheMiss(toolName);
             }
@@ -793,7 +793,7 @@ public override async ValueTask DisposeAsync()
     [LoggerMessage(Level = LogLevel.Information, Message = "{EndpointName} client resumed existing session.")]
     private partial void LogClientSessionResumed(string endpointName);
 
-    [LoggerMessage(Level = LogLevel.Debug, Message = "Tool '{ToolName}' not found in cache during tools/call. Mcp-Param-* headers will not be sent. Call AddKnownTools or ListToolsAsync to populate the cache.")]
+    [LoggerMessage(Level = LogLevel.Warning, Message = "Tool '{ToolName}' not found in cache during tools/call. Mcp-Param-* headers will not be sent. Call AddKnownTools or ListToolsAsync to populate the cache.")]
     private partial void LogToolCacheMiss(string toolName);
 
     [LoggerMessage(Level = LogLevel.Warning, Message = "Tool '{ToolName}' excluded from tools/list: {Reason}")]

tests/ModelContextProtocol.AspNetCore.Tests/AddKnownToolsHeaderTests.cs

@@ -195,6 +195,11 @@ public async Task CallToolWithoutRegisterOrList_DoesNotSendMcpParamHeaders()
         Assert.Single(_capturedHeaders);
         var headers = _capturedHeaders.Values.First();
         Assert.Empty(headers);
+
+        // Verify that a cache miss warning IS logged for HTTP transport
+        Assert.Contains(MockLoggerProvider.LogMessages, log =>
+            log.LogLevel == Microsoft.Extensions.Logging.LogLevel.Warning &&
+            log.Message.Contains("not found in cache during tools/call"));
     }
 
     [Fact]

tests/ModelContextProtocol.Tests/Client/McpClientAddKnownToolsTests.cs

@@ -408,4 +408,23 @@ public async Task AddKnownTools_NullElementInMiddle_NothingRegistered()
         var tools = await client.ListToolsAsync(cancellationToken: TestContext.Current.CancellationToken);
         Assert.Equal(2, tools.Count);
     }
+
+    [Fact]
+    public async Task CallToolWithoutCache_PipeTransport_DoesNotLogWarning()
+    {
+        // Arrange — pipe transport should NOT log a cache miss warning
+        await using var client = await CreateMcpClientForServer();
+
+        // Act — call a server tool without populating cache via ListToolsAsync
+        var result = await client.CallToolAsync(
+            ServerToolName,
+            new Dictionary<string, object?> { ["input"] = "test" },
+            cancellationToken: TestContext.Current.CancellationToken);
+
+        // Assert — call succeeds and no cache miss warning is logged (pipe transport, not HTTP)
+        Assert.NotNull(result);
+        Assert.DoesNotContain(MockLoggerProvider.LogMessages, log =>
+            log.LogLevel == Microsoft.Extensions.Logging.LogLevel.Warning &&
+            log.Message.Contains("not found in cache during tools/call"));
+    }
 }